1. Field of the Invention
The present invention relates to electrical floor polishing devices for commercial and residential use.
2. Description of the Prior Art
Many types of electrically powered floor polishing machinery have been and are presently sold in the marketplace.
The first conventional floor polishing machines, which were called "swing" machines, were very heavy and very slow. They weighed between 100 and 150 lbs. and were very difficult to transport. They generally consisted of a large D.C. rectified permanent magnet motor or a large A.C. motor mounted directly above the center of gravity of the machine. Since these machines had no wheels to support the weight of the machine while it was in operation, the total weight of the machine was transmitted to the floor through the polishing pad. Consequently, the polishing pad turned very slowly at approximately 175 rpm.
Since the "swing" machines had no supporting wheels, they were propelled over the floor by moving a handle rigidly engaged to the machine's housing up or down to swing the machine from left to right or right to left. This method of propelling the machine over the floor always required a skilled operator. Propelling the machine was complicated by the fact that the operator also needed to be proficient in removing old floor finish as well as polishing fresh floor finish. Pressure to complete jobs faster resulted in these machines reaching maximum speeds of between 300 to 400 rpm.
Increasing concern for more speed and facilitated operation resulted in a new class of divided weight machines. These machines are generally belt driven, use a set of wheels to support the motor and have a pad driving assembly which can rotate the polishing pad at between 900 to 1500 rpm. Conventionally, the pad housing is in front of the machine, the wheels are in the center of the machine and the motor is in the rear to counterbalance the pad, using the wheels as a pivot point. Conventionally, a handle is fixed to the polisher frame on housing behind these wheels. In operation, the fixed handle is used to enable continuous adjustable rotation of the pad and motor, as a counter balance, around the wheels as a pivot point to achieve maximum pad contact without overloading the motor.
Some examples of the divided weight machines are shown in U.S. Pat. No. 4,122,576 to Bevington et al. and in U.S. Pat. No. 4,756,042 to Genovese et al. These machines are an improvement over prior art "swing" machines as they can be pushed in a straight line like a lawnmower on the wheels provided.
Generally, the buffing surface of the pad defines a plane which is not tangent to the mounting wheels at their intersection with the floor surface. Consequently, with structures such as this, only a portion of the pad engages the floor. Placing the polishing pad at an angle to reduce amperage draw on a divided weight machine is shown in U.S. Pat. No. 4,122,576 cited above.
Attempts have been made to effect and maintain full pad contact with the floor by positioning the pad so that its surface does define a plane which is tangent to the mounting wheels at their intersection with the floor. However, with the operator handle generally disposed at a fixed angular relationship to the horizontal, a pushing motion upon the handle in a forward direction causes the rearward edge of the pad to be lifted from the floor, to some extent, until the inertia of the machine is overcome.
Attempts have been made to solve this problem by providing a handle which is pivotally mounted for movement about an axis on which the mounting wheels rotate. As the operator applies force to the machine by pushing it in a forward direction, some of the force is attenuated by the handle pivoting about the axis, and not as great a tilting movement is imparted to the buffing pad. Consequently, a greater percentage of the pad's surface will stay engaged with the floor than would if the handle was mounted at a fixed angle. An example of this type of machine is shown in U.S. Pat. No. 4,115,890 to Burgoon.
In all of the structures heretofore described, however, disengagement of at least a portion of the pad will always occur, at least for a short period of time, to one degree or another.
Whether an angle is purposely placed on a rapidly rotating disc or when propelling the machine forward, problems are created. When the extra pressure of an angled pad is placed on the front of the machine, the machine torques very hard to the right or to the left depending on which way the pad is turning. When the extra pressure falls either to the right or to the left side of the machine, it will buff bright one side and dull on the other. This, of course, makes use of the full potential of these machines impossible.
An additional improvement to divided weight machines, is found in U.S. Pat. No. 4,358,868 to Cook. As the polishing pad in contact with the floor becomes thinner due to wear, the increased angle on the pad causes increased torque and polishing problems of the type identified above. U.S. Pat. No. 4,358,868 addresses this problem by providing a mechanical device that manually raises and lowers the angle of the machine frame by moving the wheels up and down in slots placed in the frame. Accordingly, as the pad grows thinner from use, the angle could be compensated by the turning of a knob. While this device partly corrected some of the problems of divided weight machines, it clearly does not address the inherent problems identified above.
U.S. Pat. No. 4,365,377 to Todd et al. responds to the problems presented by divided weight machines by providing a third support in the form of a caster as a supplement to the wheels. The caster is located at the center of the polishing pad. In this way, the invention intends to permit full pad surface engagement. However, since the caster is spring-biased, any unevenness encountered by the caster in the floor results in uneven distribution of the weight of the machine to pad. Indeed, a deep indentation in the floor would result in a severe amperage draw which would overheat the motor.
The problems with all conventional divided weight machines can be attributed to the state of motor technology at the time of their concept. These motors were generally heavy, weighed between 30 to 60 lbs. and rated at 11/2 H.P. with an efficiency rating below 85%. These characteristics barely permitted machines using such motors from performing the tasks required. To compensate for these motor features, the divided weight machines are all designed to take weight off the polishing pad to avoid motor slow-down and the drawing of more amperage which hampered the polisher's effectiveness.
It is to these deficiencies in the art that the invention, in accordance with the present application, is directed. It provides a combination of structural elements including the use of new brushless D.C. motor technology and features which permits the machine, as it is propelled forward, to eliminate any lifting of the polishing pad around the wheels while maximizing full engagement of the buffing or polishing surface of the pad with the floor.